1. Field of the Invention
This invention relates to sheaths for use with catheters and more particularly to flexible sheaths used in the percutaneous method of introducing catheters.
2. Description of the Prior Art
Insertion of catheters into blood vessels is frequently accomplished percutaneously, a term indicating that surgical cut-down to the vessel is not employed, but rather the initial entry into the vessel is by direct needle puncture through the skin. Early practise employed the puncturing needle itself as a direct conduit to the blood vessel for a catheter of sufficiently small diameter to be passed inside the needle. At first, such catheters were of adequate length to permit the needle to be withdrawn entirely from the tissue yet remaining on the proximal portion of said catheter outside the human body. However, the needle so remaining on the catheter was often an impediment, hence the desirability of freeing the needle completely from the catheter was recognized.
Subsequent art developed the longitudinally split needle which separated into two distinct members. This was possible owing to the physical properties of steel, including strength, rigidity, and precise machinability so that minute mechanical features of the two parts enabled them to snap together or otherwise securely engage and capture one another in order to function as a one-piece needle.
The foregoing metallurgical and mechanical art was not applicable to thin-walled plastic sheaths, as subsequently used for the percutaneous insertion of large-diameter cardiovascular catheters according to the method of Seldinger as modified by Desilets and Hoffman described in Timmerman's U.S. Pat. No. 4,581,025. Therefore, such sheaths often remain in place during catheterization procedures, or may be drawn back along the catheter if removal from the puncture site is desired. However, the hub (e.g. LUER-LOK or bayonet fitting) at the proximal end of the catheter prevents removal of the sheath from the catheter itself.
In those instances where intravascular catheters remain in place for longer periods of time, or are to be permanently implanted as with pacemakers, it is desirable to remove the sheath completely. This led to the development by Littleford and others of the "peel-away" sheath, a very flexible and flaccid, thin-walled plastic tube without any proximal hub or fitting, whose proximal end was already bi-leaved so that grasping one such leaf in each hand and pulling apart caused the sheath to tear longitudinally along opposite lines and separate into two long strips. This sheath is described in Timmerman's U.S. Pat. No. 4,581,025. While accomplishing its objective of removing the sheath, it is a cumbersome method because both hands must grasp the sheath, leaving the catheter within said sheath unattended unless an assistant is present. Also once removed, another sheath cannot be inserted over the catheter if so desired.
Another disadvantage of the presently-used sheaths results from the fact that they are of fixed diameter. Thus, when percutaneous insertion is performed, a sheath is inserted which will accommodate the largest-diameter catheter needed during the procedure. Further, all catheters used during the procedure should match the diameter of the largest catheter needed, since the lumen of the sheath must be fully occupied to prevent excessive bleeding. For example, measurement of intracardiac blood pressure or injection of small volumes of radio-contrast dye into the coronary arteries can be adequately performed with a catheter of diameter significantly smaller than that needed for injection of a large volume of dye to visualize the left ventricle; thus, the greater portion of such a complex procedure could be performed via a small puncture hole, and only at the end of said procedure need the puncture hole be dilated, which so executed would reduce the degree and incidence of postprocedure bleeding. However, employing sheaths of fixed diameter only permit catheters of identical diameter to be deployed via said sheath.
Other patents which deal with sheaths include U.S. Pat. No. 3,401,687 to Hood which discloses a sexual aid for males comprised of an expansible unitary resilient member with overlapping ends. U.S. Pat. No. 4,581,025 to Timmermans teaches a tear away sheath of the type generally employed in the prior art. U.S. Pat. No. 4,602,624 to Naples et al. discloses a nerve cuff which uses a self-curling sheet of non-conductive material biased to curl into a tight spiral.